As disclosed in Patent Documents 1 and 2, for example, there is a known litter system for a pet animal having two-tired structure of a floor material for urination and a urine-absorptive material so as to prompt excretion on the floor material for urination, and to absorb urine passed through the floor material for urination on the absorptive material.
Pet animals are fond of excreting on a sandy article in habit. Therefore, in Patent Documents 1 and 2, granular materials allowing urine to pass through rather than absorbing it is spread as the floor material for urination. The floor material for urination is arranged in the upper tier to prompt a pet animal to access the litter and to excrete, and the urine is absorbed by absorptive material in the lower tier.
In Patent Document 1, plant-derived crushed pieces and synthetic resin powder are mixed under stirring to mold into grains. The synthetic resin powder is molten by heat spontaneously generated during molding with a molding machine so that the plant-derived crushed pieces are bonded together due to the melt so as to attain urine absorption inhibitory effect and shape retentivity ensuring the crushed pieces not to be collapsed even if urine is absorbed.
In Patent Document 2, there is described a method for allowing urine passing through the floor material for urination without being absorbed by using mineral sand such as river sand for the floor material for urination, and applying a water repellent coating such as silicon or wax to the sand.
Patent Document 1: Japanese Patent No. 3519353
Patent Document 2: Japanese Patent Application laid-Open No. 7-67489